The typical epicyclic gear system has a sun gear, a ring gear surrounding the sun gear, and several, often three, planet pinions located between and engaged with the sun and ring gears, and in addition, it has a carrier that is coupled to the planet pinions to establish axes about which they rotate. A gear system so configured splits the torque transferred through the system into load paths equal in number to the number of planet pinions. This reduces the forces at each mesh and enables the system to transfer a large amount of power in a relatively compact configuration. In other words, it provides a high power density.
Often the ring gear remains fixed, leaving the carrier and sun gear to rotate. In such an arrangement, power may be applied at one end of the carrier and delivered through the sun gear at a different velocity and torque. This holds true for the transmissions in wind turbines that harness the energy of the wind and convert it into electrical power.
Many epicyclic gear systems utilize a straddle-type carrier in which the planet pinions rotate between two walls on pins that extend between the walls, each pin being affixed at both of its ends in the walls. When torque is applied to the carrier at one of the end walls, the carrier will twist and advance one end of each pin ahead of the other. This skews the planet pinions with respect to the sun and ring gears and disturbs the mesh between the planet pinions and the sun and ring gears.
An epicyclic gear system in which the planet pinions are supported on and rotate about so-called “flexpins” helps mitigate unequal load distribution around the planet pinions and skewing of the pinions as well. In this regard, a flexpin for a planet pinion at one end is attached to and cantilevered from a single wall of the carrier of which it is a part. The other end of the flexpin has a sleeve fitted firmly to it, with the sleeve extending back over and otherwise being radially spaced from the flexpin. The sleeve forms part of or carries a bearing that supports one of the planet pinions. At the carrier wall the flexpin bends in one direction circumferentially relative the central main axis of the system and at its opposite end bends in the other direction, again circumferentially, all such that the sleeve axis remains parallel to the main axis. In other words, flexpin technology employs a double cantilever to equalize load distribution and to offset the skewing that would otherwise occur.
Each flexpin, its sleeve, sometimes the planet pinion that surrounds the sleeve, and the bearing located between the sleeve and the planet pinion forms a flexpin assembly. Typically, the bearing is a double row antifriction bearing. The outer raceways for the bearing may be integrated into the planet pinion. The inner raceways may be integrated into the sleeve to provide an integrated flexpin assembly. Here, instead of a cross section that includes both the sleeve and separate inner races, the cross section has just the sleeve and is somewhat smaller. However, the bearing has an initially separate rib ring to facilitate assembly. Once assembled, the ring is welded to the sleeve, and its axial position determines the setting for the bearing. See U.S. Pat. Nos. 7,056,259 and 6,994,651. The integrated flexpin affords more space for the rolling elements, so that rolling elements of greater diameter may be employed, and this increases bearing capacity. Also, an integrated flexpin normally operates with a planet pinion that has outer bearing races integrated into it. This increases the radial cross sections between the roots of the teeth on the planet pinion and the outer raceways (greater rim thickness). Moreover, an integrated flexpin has fewer components, thus simplifying the design and making it easier to manufacturer.
The use of the pin with groove, coupled with a welded rib ring on the sleeve to achieve roller retention and bearing adjustment, also results in a very short flexpin assembly, which in some cases can lead to a reduction in gear box length and thus reduce overall weight and cost. See U.S. Pat. No. 6,994,651.
However, a fully integrated flexpin with its welded rib ring is not easily serviced. Indeed, to replace the planet pinion or a component of the bearing, the flexpin of the assembly must be separated from the remainder of the carrier, usually a carrier wall in which the flexpin is secured with an interference fit. The elevations at which wind turbines operate exacerbate the problem.